1. Field of the Invention
This invention relates in general to an electrode substrate of a plasma display panel (PDP) having a tiny and high-precision electrode pattern. More specifically, the invention relates to a manufacturing method for an electrode substrate of a plasma display panel (PDP) that is capable of precisely and inexpensively making the electrode pattern.
2. Description of Related Art
Conventionally, the brown tube (cathode ray tube, CRT) or liquid crystal display (LCD) is widely used in display device, such as color television or personal computer. However, there are certain limitations on miniaturization and rarefaction due to their structures.
On the other hand, plasma display panel (PDP) is recently noted for replacing the foregoing displays. The PDP can be used for providing a very thin display device because the pixels are self-emitting type. Furthermore, in comparison with the LCD, the PDP structure is simpler and thinner, and therefore it is easily to achieve a large screen. Accordingly, the huge demand for PDP as the next generation display is anticipated. However, the manufacturing cost for a PDP is very high at present, which is a barrier to commercialize the home-oriented display device.
FIG. 1 shows an exemplary perspective view of a rear substrate of a plasma display panel. As shown, the PDP is composed of a rear substrate having an address electrode (Ag) 10, a dielectric layer (glass) 16′ and a passivation layer (MgO) 17′, and is combined face-to-face with a front substrate 18 that has a transparent electrode 14, a bus electrode 15, a transparent dielectric layer 16 and a passivation layer (MgO) 17. The rear electrode 10, ribs (spacers) 12 and fluorescent layers (R, G and B) 13 are formed on the rear electrode 10.
Conventionally, the electrodes are formed by coating the silver paste (for example, “fodel®” registered by Dupont) with a predetermined thickness (5–10 μm) on the whole rear substrate, and then the silver paste is patterned by drying, exposure and development. The electrodes are also formed by adhering a photosensitive silver tape on the front substrate and then patterned by exposure and development. Namely, the electrode pattern is formed by the photolithographic method.
However, when the line width of the pattern complies with the requirement of the electrode, the line width is 50–70 μm and the corresponding pitch is about 350 μm. The amount of the removed silver paste in the developing process would be too much and would not be economical. The removed silver paste must be recycled and reused because low utilization rate of the silver paste and high manufacturing cost of the electrode are highly related. However, there are no effective methods for solving the cost issues in the recycle and reuse processes.
Additionally, in order to increase the opening rate at the front substrate, forming an electrode pattern that has a width thinner than 2˜50 μm is required. Furthermore, from the aspect of suppressing the light reflection, not only the pattern composed of silver, but the silver pattern containing black color has to be provided at the same time. Therefore, it becomes more obvious that the paste utility rate is low and the manufacturing cost increases.
The apparatuses used in the series of processes of exposure, development and drying of photolithography require very high precision and cleanliness. Moreover, because a large amount of harmful liquid waste is generated, burdens to the environment and the processing of the liquid waste become large. Therefore, the manufacturing of electrode by photolithography is very disadvantageous in the aspect of cost.
In order to solve the issues above, the inventor repeatedly studies and discusses the use of the printing method for replacing the photolithographic method such that the electrode pattern of a PDP panel can be inexpensively formed.
Conventionally, the printing method is not suitable for forming a very tiny and highly precise pattern for the PDP electrode. In addition, among the various printing methods, even though the intaglio offset printing method that is the most superior in printing accuracy is used, it still has a drawback (pinhole) that the printing shape deteriorates due to the repeated printing. Also, from the point of view of productivity, it is very difficult to use the printing method for making the electrode substrate for a PDP panel.
However, the inventor repeatedly studies and finds that the electrode pattern can be made by printing with a conductive ink containing metal powder to form a conductive pattern, and then baking the conductive pattern to form the electrode pattern.
As a result, even though it is conventionally very difficult to form a tiny pattern with a highly precise printing method, a completely unexpected new fact is discovered that a very tiny and highly precise electrode pattern, meeting the requirements of a PDP panel, can be made by the printing method when the intaglio offset printing is used as the printing method, wherein the solvent of the conductive ink and the rubber material used as the surface layer of the printing blanket are suitably combined to meet the swelling degree relative to the solvent of the rubber.
In addition, to form an electrode pattern of a PDP panel using the printing method is a result of repeatedly diligent study. Even though the printing method is used for forming a conductive pattern, a very tiny and highly precise electrode pattern can be formed. To form a very tiny and highly precise electrode pattern that meets the requirements for the manufacturing of an electrode substrate of a PDP panel, the intaglio offset printing method is used and the printing blanket used for transferring the conductive ink is heated after one or several times of printings are finished under a predetermined condition to vaporize the solvent of the ink that is immersed into the surface of the printing blanket. Furthermore, an increase in the productivity and an inexpensive manufacturing of the electrode substrate of the PDP panel are achieved.